If there are custom fields that are not used e.g., optional, in all entries, does this in any way affect performance? I am considering implementing a somewhat monolithic custom fieldset to be associated with various channels.
For each custom field you add, it adds at least 2 columns to the
exp_channel_data table, and if that table gets too big, it can affect performance in some respects.
I have a site with many channels and many fields, and my
exp_channel_data table is up to 600 columns. This becomes a problem when I want to add new custom fields. I have over 200k+ entries in that table, and it now takes several minutes to add a new custom field.
I haven't, however, noticed any major issues with the reading of the data... just the actions that require modifications to that table. Hope that helps some!